In DW concept the source file is the one provided by the user or OLTP system and is extracted by scripts feed in to ETL system for processing. So it is to be taken as input and to output/populate.
If this question means creating dummy records for parallel jobs then
1. need to load the proper metadata to the row generator stage 2. and then supply the criteria and conditions like how the data should look like. for ex if its numeric value we can specific like the range starting values end values and etc.
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